Under certain operating conditions, engine cylinders can misfire or have slow burns. These misfires or slow burns can increase hot residuals entering an adjacent cylinder during cam or valve overlap periods. When this happens, the hot residuals can cause the misfire to pre-ignite within the adjacent cylinder. The pre-ignition can generate very high in-cylinder pressures that can result in combustion pressure waves similar to combustion knock, but with larger intensity.
Also, in boosted engines, late burn combustion events wherein the combustion is later than intended can also lead to pre-ignition combustion events. Specifically, the late combustion can lead to high exhaust manifold pressures and temperatures, as well as higher than intended exhaust residuals. The elevated exhaust manifold pressures can overcome the exhaust valve spring pressure and potentially open exhaust valves on adjacent cylinders, filling the cylinder with hot exhaust gas residual and increasing the likelihood of pre-ignition in the adjacent cylinders. The issue may be exacerbated in small volume exhaust manifolds, such as may be used in turbocharged engine systems to minimize the time to torque. As such, pre-ignition events can reduce engine performance and cause engine degradation.
The inventors herein have recognized that some of these issues may be at least partly addressed by a method for an engine, comprising: in response to misfire or at least a partial burn in a first cylinder, selectively deactivating spark ignition to a second cylinder receiving exhaust residuals from combustion in the first cylinder. In this way, late burn induced pre-ignition events may be reduced.
In one example, a misfire event, partial burn, or late combustion event in a first cylinder may be determined based on crankshaft acceleration, spark plug ionization current, cylinder pressure data, exhaust air-fuel ratio, etc. A second, neighboring cylinder that is most likely to receive exhaust residuals from the first cylinder may then be identified based on the identity of the first cylinder, the firing order of cylinders on the engine, as well as a configuration of the engine's exhaust manifold. In response to a misfire or late combustion event, a pre-ignition mitigating action may be performed in the second cylinder to reduce the likelihood of pre-ignition being induced in the second cylinder due to the late burn event in the first cylinder. This may include selective and temporary suspension of spark and fuel injection to the second cylinder. In some examples, only spark may be disabled, such as when the late combustion event is less retarded from a threshold timing or when the likelihood of pre-ignition in the second cylinder receiving the exhaust residuals is lower. The spark and/or fueling may be disabled for the combustion event in the second cylinder and then re-enabled for the immediately subsequent combustion event.
Further still, the pre-ignition mitigating action of disabling spark and/or fuel injection may be extended to additional cylinders. For example, a third cylinder that is most likely to receive exhaust residuals from combustion in the second cylinder may also have spark and fuel disabled, to reduce the likelihood of pre-ignition in the third cylinder due to hot residuals received from the second cylinder, and so on.
In this way, by deactivating spark and fuel injection to one or more cylinders likely to (progressively) receive exhaust residuals from late combustion in a neighboring cylinder, a temperature and pressure of the exhaust residuals may be decreased. By reducing the temperature and pressure of the residuals, the likelihood of pre-ignition induced in a cylinder due to receipt of hot exhaust residuals from a late burning or misfiring cylinder may be decreased. In addition, the likelihood of pre-ignition being induced in further cylinders by combustion in the cylinder receiving the hot residuals is also reduced. Overall, engine degradation due to pre-ignition can be mitigated.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.